Simplified multi-beam cylindrical array antenna with focused azimuth patterns over a wide range of elevation angles

ABSTRACT

A simplified multi-beam cylindrical array antenna system in which the feed and scanning system is simplified. Radiator elements grouped into columns are fed by a beam-forming matrix which has a number of input ports, each corresponding to a discrete elevation beam angle. The ports of the beam-forming matrix are grouped together in zones, each zone being fed by a combining network having a single common or input terminal. In this way, a smaller number of azimuth scanning feed matrices corresponding to the number of combining networks is required. Thus, a fan-shaped beam (in elevation) is formed and may be scanned in azimuth. The focusing quality of the said fan beam is better than obtainable with the prior art &#39;&#39;&#39;&#39;separable&#39;&#39;&#39;&#39; technique and approaches that of the &#39;&#39;&#39;&#39;independent&#39;&#39;&#39;&#39; technique, while requiring comparatively little additional equipment than necessary in the simpler, so-called &#39;&#39;&#39;&#39;separable&#39;&#39;&#39;&#39; technique.

States atent Charlton [451 Mar. 28, 1972 [21] Appl. No.: 101,300

52 use: ..343/854,343I876 [5i] lnt.Cl. ..H01q3/26 5s Fieldoi'Search ..343/776,777,778,779,754,

[56] References Cited UNITED STATES PATENTS 3,568,207 3/1971 Boyns ..343/854 Primary Examiner-Eli Lieberman AttorneyC. Cornell Remsen, Jr., Walter J. Baum, Paul W. Hemminger, Charles L. Johnson, Jr. and Thomas E. Kristofferson [5 7] ABSTRACT A simplified multi-beam cylindrical array antenna system in which the feed and scanning system is simplified. Radiator elements grouped into columns are fed by a beam-forming matrix which has a number of input ports, each corresponding to a discrete elevation beam angle. The ports of the beam-forming matrix are grouped together in zones, each zone being fed by a combining network having a single common or input terminal. In this way, a smaller number of azimuth scanning feed matrices corresponding to the number of combining networks is required. Thus, a fan-shaped beam (in elevation) is formed and may be scanned in azimuth. The focusing quality of the said fan beam is better than obtainable with the prior art separable" technique and approaches that of the independent" technique, while requiring comparatively little additional equipment than necessary in the simpler, so-called separable" technique.

8 Claims, 4 Drawing Figures ELEV 9770M DISTRIBUTION flZ/MUTH FEED AND SCANNING MATRIX NETWOZK BEQM 3, FDCUSED HT ELS 55 1MB FOCUSED HT EL 2 BEA/M1 FOCUSED 07' EL 1 PTENTED MR 2 a 1972 SHEET 2 [1F 2 LILIPPPIFP LLJN FFFFFFFFF-FH BEG/V) 3, FDCUSED QT ELS 550M 2, FOCUSED 0T EL 2 ELEVATION BEAM FORM/N6 NETWORK ,QA/D RAD/A7025 559M P060550 5L 1 INVENTOR. GREGORY 6. CHQELTON SIMPLIFIED MULTI-BEAM CYLINDRICAL ARRAY ANTENNA WITI-I F OCUSED AZIMUTH PATTERNS OVER A WIDE RANGE OF ELEVATION ANGLES BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to antenna systems, and more particularly, to electronic scanning cylindrical arrays most useful in the microwave region.

2. Description of the Prior Art In the prior art, cylindrical array antennas have been used where their inherent symmetry and capability for 360 scanning or pattern rotation is required. Cylindrical antennas also are known for the relative ease with which inertialess (electronic) scanning can be applied to them.

One example of a prior art cylindrical array antenna system is described in U.S.'Pat. No."3,474,446. That device is concerned mainly with the development of a rotating gearshaped" azimuth radiation pattern for use in a particular type of air navigation system. In other applications, a pencil beam or vertical fan beam may be required to be developed by the array and scanned rapidly in azimuth over the total 360. In such applications, the requirements frequently involve a narrow azimuth beam width (about l or 2) with a low order of sidelobes (below l8 db.) which do not appreciably vary as the beam is scanned. Coverage over a range of elevation angles is also frequently required, with little or no variation of azimuthal characteristics.

Cylindrical array antenna systems usually considered for scanning systems fall into two main categories. The first is a simple separable ring with column feeds, where each ring (or column) has the same excitation as the other excited rings (or columns). The other category comprises the complex independent clement feed arrangements, where each element in the array is independently controlled in amplitude and phase. Both these categories can be achieved without requiring any circuit losses to be included in the ideal sense.

With the simple separable ring and column feed system, the horizontal ring excitation, in amplitude and phase, is formed independently of the vertical column excitation. in the horizontal ring feed, provisions for stepping and/or scanning the beam 360 in azimuth, can be included in the form of a matrix feed. Such a matrix feed has the capability for switching the excitation around the aperture one column at a time, thus maintaining the pattern shape. A single ring feed for any arbitrary number of elements in a column follows from this relatively simple approach. The column feed is constructed of passive elements to provide the required vertical fan beam. The inherent disadvantage of such a system is that the vertical fan beam does not retain its azimuthal characteristics constant at all elevation angles. That is to say, the beam is not uniformly focused over its entire elevation angular coverage. This effect is caused by defocusing phase errors introduced by the geometry of the cylinder and is a fundamental property of a cylindrical array antenna. An illustration of this prior art effect is included in the drawings accompanying this specification.

The aforementioned more complex independent" cylindrical array antenna system includes an independent element feed and amounts to a brute force" approach, in that every radiating element is controlled independently in amplitude and phase. Such an approach completely eliminates the defocusing problem associated with the simpler separable technique, and accordingly, it could be regarded as the theoretically ideal approach. The implementation of such a technique is, however, a very great task, results in a very large amount ofequipment, and is, therefore, very expensive.

In the implementation of the independent element feed system, programming means must be provided so that the excitation can be varied in an unusual pattern in amplitude and phase. Moreover, this excitation must be switched around the cylinder to provide 360 of scanning. A switching matrix, equivalent to the matrix in the so-called separable" technique, is required for each and every ring of elements in the array. Thus, for a cylindrical array with 20 elements in a column, 20 separate switching matrices would be used to scan the beam. It will be realized that such a system is much too expensive to be considered practical, except in the most demanding and sophisticated situations where cost is not a prime consideration.

The manner in which the present invention overcomes the disadvantages of the aforementioned prior art approaches to the cylindrical array development problem will be fully understood as this specification proceeds.

Certain components or subassemblies of the novel combination of the present invention are of themselves prior art and these are described with citation of suitable descriptive references for those known elements or subassemblies.

SUMMARY OF THE INVENTION In accordance with the aforementioned disadvantages of the prior art systems, it may be said to have been the general objective of the present invention to produce a simplified multi-beam cylindrical array antenna which performs much better than the separable" arrangement, and approaches the performance obtainable with the so-called independent" technique while requiring only a small increase in complication over the relatively simple separable" approach.

The multi-beam cylindrical array antenna feed and scanning concepts included in this invention provide an approximation to the ideal excitation afforded by the independent" technique using a network to drive the radiating elements which is just slightly more complex than that required for the simple separable" technique. The ability to achieve this result without requiring any circuit loss is retained.

The present invention is subject to variations within the concepts.

In the most complicated form of the present invention, each column drive would consist of a complete beam-forming matrix with N input beam ports and N output radiating element connections. Each port would form a horizontal fan beam at different elevation angle. Combining fan beams generated at the same elevation by each column by means of an azimuthal ring feed, results in a pencil beam at that elevation angle. Moreover, there will be a separate beam-forming matrix port representing each discrete elevation beam angle. Each pencil beam thus generated is, of course, focused for its particular elevation angle. Furthermore, each pencil beam could, in a system of that type, be independently presented or generated contemporaneously in order to form a merging of beams to provide a vertically oriented fan beam pattern; still preserving the separate port concept thus applicable to each separate beam or each elevation angular level or zone within the composite fan beam. The individual columns of radiators acting as linear arrays cooperate with adjacent columns over the cylindrical array aperture to combine beams with the required amplitude in phase to form the desired vertical fan beam.

An azimuth feed and scanning matrix applicable to each corresponding level (zone) of beam forming matrix ports, provides for azimuth scanning in accordance with means to be described in more detail as this specification proceeds.

A very important aspect of the present invention is its adaptability to simplification by grouping together beamforming matrix ports, forming zoned portions of the elevation fan beam into fewer ring feeds and azimuth scanning matrices. As a first simplification, consider the upper and lower ports of the beam-forming matrix (which may be a Butler matrix, or the so-called equal path length beam-forming matrix using crossed-line directional couplers) which are used to form the elevation sidelobes of the elevation fan beam. These sidelobe ports can use the same ring feed (azimuth feed and scanning matrix) as the adjacent port that forms a portion of the required fan beam shape. The sidelobes will, in that case, be defocused in azimuth which will tend to suppress their level.

This simplification reduces the number of total vertical ports as well as the number of ring feeds and azimuth scan matrices included with them. For example, for a cylindrical array having 20 elements in a column, only 6 total ports, ring feeds and scanning matrices are needed to form a shaped fan beam over about a 34 elevation angle.

In the hereinabove example, each of the 6 beams, forming the total shaped fan beam and elevation is focused in azimuth by using separate ring feeds, resulting in ideal focus about every 5.7". Observing that, for most cylindrical arrays, the amount of defocusing over 5.7 range is slight, it will be realized that the number of beam ports and ring feeds can be further reduced. If only 3 beam ports and ring feeds are used, each with two adjacent beams, then the perfect focusing angles are about I 1.4 apart. The resulting simplified muIti-beam cylindrical array antenna affords a very substantial improve- 'm'ent over the aforementioned fseparable" technique array drive arrangement.

The manner in which the component electrical arrangements and connections within the microwave circuits of the preferred embodiment of the present invention are effected will be better understood as a detailed explanation is hereinafter undertaken.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an Equi-Powe'r Contour illustration for a prior art cylindrical array antenna using a separable ring and column feed arrangement to show'the inherent defocusing problem;

FIG. 2 is a functional block diagram illustrating the principles and connections of a system in accordance with the present invention;

FIG. 3 is a typical end-on view ofa fan beam composed of3 pencil beams in accordance with the present invention; and

FIG. 4 is a more detailed showing of the beam-forming network connections within the device of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, a self-explanatory diagram is presented illustrating the defocusing (beam broadening) effect encountered in the so-called prior art separable technique as applied to a cylindrical array. The equal power contour lines are shown as viewed looking radially into a typical shaped beam cylindrical array antenna. In the example of FIG. 1, the array was focused in azimuth at an average elevation angle; however, significant defocusing takes place as the elevation angle departs from this design angle to either side of this arbitrarily selected elevation angle. The actual amount of defocusing, of course, depends on the radius of the cylinder, the width of the sector of concern and the wavelength of operation. Nevertheless, the defocusing effect illustrated is pertinent for a typical situation and a typical combination of physical parameters.

Referring now to FIG. 2, a functional and structural block diagram of a preferred embodiment of the present invention is presented. A number of identical network column feed assemblies, of which is typical, are distributed about the array aperture. Each of these columns has a plurality of radiating elements illustrated as dipoles, typically 30. It should be understood that the representation of a dipole is typical only, other types of radiators, such as slots of the various types, are frequently employed in this art, and are entirely consistent with the concept of the present invention. The element 10 referred to on FIG. 2 as an elevation beam forming network and radiators, is shown in more detail in FIG. 4. Suffice to say at this point in the description, that each of the three combination ports 16, 17 and 18 correspond to suitable feeds within 10 for producing the respective beams a, 15b and 150.

Each of the three ports 16, 17 and 18 is fed from a separate azimuth feed and scanning matrix, correspondingly 11, 12 and 13. Thus, these three azimuth feed and scanning matrices ll, 12 and 13 each have a number of terminals identified as terminals 19 through 25. On 11, for example, the terminals 19,

20, 21, 22 and 23 represent only a portion of the total number of output ports that device 11 would have, the said total number of ports corresponding to the actual number of network and radiator blocks 10 distributed around the total cylindrical array. In the illustrated case, the three input ports 16, 17 and 18, for the device 10 are typically fed from 21, 24 and 25, respectively, from the corresponding ones of I 1, l2 and 13. It will be seen from the foregoing, that three zones of elevation plane feed have thus been established, these corresponding directly to the three beams illustrated generally at 15.

In order to reach the common antenna system terminal 34, the one remaining element consists of the elevation distribution network 14. This device is merely a combining circuit or branching network. Such devices are known and used, for example, for the feeding of subarrays from a common line. Such a device instrumented in wave guide is illustrated in FIG. 49,

Pages 11-61 of Radar Handbook" by Merrill I. SkoInik (1970), a McGraw Hill book. The three terminals 31, 32 and 33 of the device 14, are connected to the common terminals (ports) of the devices 11, 12 and 13, respectively. It will be seen that 33 is connected to 26, the port or terminal of 13, and 31 and 32 are similarly connected to l 1 and 12.

Concerning the details of instrumentation of each of ll, 12 and 13, a suitable subsystem for this purpose is described in a paper entitled: An Electronically-Scanned Cylindrical Array Based On a Switching-and-Phasing Technique by Richard .I. Giannini. This paper was published in the program and digest of the 1969 International Symposium of the IEEE Group on Antennas and propagation (IEEE Catalog No. 69 C-53-AP). While the device described in that reference is intended for monopulse operation in which the common terminal includes both sum and difference lines, it is readily adaptable to the instrumentation of 11, 12 and 13. Functionally, each of the devices 11, 12 and 13 may be said to produce a programmed, rotating synchronous column excitation. If it were assumed, for example, that column 10 received the maximum azimuth excitation (in three elevation zones) at any one time, adjacent columns would be excited at lower levels and in phases appropriate for beam focusing on each of the three beams.

FIG. 3 is entirely self-explanatory when related to the beams, generally at 15, in FIG. 2. The nature of an elevation fan beam synthesized in the manner of this invention is better understood from F IG. 3.

Referring again to FIGS. 2 and 4, the actual number of radiating elements in a column is, of course, a design matter and not a basic consideration in the present invention.

In FIG. 4, a beam forming matrix 10a is shown. This device can be any one of several microwave circuits capable of providing the function. Basically, it is a muIti-port device which positions a beam from the associated linear array (column of radiating elements) at a different discrete angle according to which port is excited. In the aforementioned Radar Handbook," two devices, either of which is capable of providing that element of the structure of FIG. 4, are shown in FIG. 57 (Pages 11-66). One is the so-called Equal Path Length Beam-Forming Matrix, and the other is the so-called Butler Matrix. Both are well known per se in this art.

The beam ports of such a beam-forming matrix are combined into three zones in accordance with the hereinbefore described theory of this invention. In FIG. 4, three branch (combining) circuits 27, 28 and 29 are employed). These are equivalent in structure to the device 14 and functionanalogously.

The grouping of the ports of 10a in FIG. 4 is, of course, illustrative only, as are the number of array elements and the actual number of zones corresponding to terminals 16, 17 and 13.

Those skilled in this art will recognize the possibilities for up or down scaling of the structure of the invention, and also for other modifications and variations within the scope of the invention. For one example of a variation which can be constructed from knowledge of this art, the signals traveling between ports 16, 17 and 18 and the radiating elements 30,

may be obtained by a combination device which will combine the circuitry of 27, 28 and 29 with the matrix a thereby reducing the total number of components and the cost. Accordingly, the scope of the appended claims is not to be considered limited by the drawings and this description, these being illustrative and typical only.

What is claimed is:

1. In a cylindrical antenna array system which includes a plurality of radiating elements circumferentially spaced in rows and columns and a plurality of beam-forming matrices, one for each of said columns of radiating elements, each of said beam-forming matrices having a descrete output connected to each of said radiating elements in a corresponding column to form a pattern composed of a combination of individual pencil beams at discrete angles in the direction of the axis of said cylindrical array, the combination comprising:

a plurality of feed and scanning matrices for feeding said beam-forming matrices in a sequence in a plane orthogonal to said axis to produce scanning in said orthogonal plane;

a plurality of combining circuits for assembling the feeds of said beam-forming matrix ports into adjacent groups each of an independent predetermined number of said ports, said combining circuits each having a combining circuit common feed terminal;

and means for feeding said beam-forming matrices through said combining circuit common feed terminals, thereby to reduce the number of said feed and scanning matrices.

2. A multi-beam cylindrical array antenna system comprisa plurality of radiating elements spaced in rows and columns about said cylindrical array, said columns extending in the same direction as the axis of said cylindrical array;

a plurality of beam-forming networks, one for each of said columns of radiating elements, each ofsaid beam-forming networks having a discrete output connected to each of said radiating elements in a corresponding column, each of said beam-forming networks also having a plurality of input ports each corresponding to a discrete beam angle in an axial plane containing said cylindrical axis and the corresponding column;

for providing independent column zone feed means comprising a plurality of combining networks each having an input and a plurality of outputs, said outputs being interconnected with a predetermined plurality of adjacent input ports of a corresponding one of said beam-forming networks; scanning means comprising a plurality of orthogonal plane feed networks, each of said orthogonal feed networks having an input terminal and a plurality of output terminals each corresponding to a discrete beam angle measured in a plane substantially at right angles to said axis of said cylindrical array, each of said output terminals being connected to said input of one of said first combining networks corresponding to a discrete one of said column zones, thereby to produce a predetermined radiation pattern in said orthogonal plane; and means comprising a distribution network for connecting said orthogonal feed network input terminals to a common antenna system radio frequency terminal. 7

3. The invention set forth in claim 2 in which said axis of said cylindrical array is substantially vertically oriented whereby said beam angles in said axial plane are elevation angles and said plane substantially at right angles to said axis is the azimuth plane.

4. The invention set forth in claim 3 further defined in that the number of said combining networks and the number of said orthogonal plane feed networks and therefore the number of said independent column feed zones are all equal.

5. Apparatus according to claim 4 in which said plurality of orthogonal plane feed networks is small compared to the number of ports of said beam-forming networks.

6. Apparatus according to claim 5 in which the number of input ports of said beam-forming networks combined in each of said combining networks is substantiall equal.

7. Apparatus according to claim 5 m w lch said beam-forming networks are Butler matrices each having a number of said input ports equal to the number of radiating elements in the corresponding column.

8. Apparatus according to claim 5 in which said beam-forming networks are series fed, equal path length beam forming networks having a predetermined number of ports and therefore being capable of providing a corresponding number of discrete elevation beam positions, said ports being fewer in number than the number of said radiating elements in the corresponding column. 

1. In a cylindrical antenna array system which includes a plurality of radiating elements circumferentially spaced in rows and columns and a plurality of beam-forming matrices, one for each of said columns of radiating elements, each of said beamforming matrices having a descrete output connected to each of said radiating elements in a corresponding column to form a pattern composed of a combination of individual pencil beams at discrete angles in the direction of the axis of said cylindrical array, the combination comprising: a plurality of feed and scanning matrices for feeding said beamforming matrices in a sequence in a plane orthogonal to said axis to produce scanning in said orthogonal plane; a plurality of combining circuits for assembling the feeds of said beam-forming matrix ports into adjacent groups each of an independent predetermined number of said ports, said combining circuits each having a combining circuit common feed terminal; and means for feeding said beam-forming matrices through said combining circuit common feed terminals, thereby to reduce the number of said feed and scanning matrices.
 2. A multi-beam cylindrical array antenna system comprising: a plurality of radiating elements spaced in rows and columns about said cylindrical array, said columns extending in the same direction as the axiS of said cylindrical array; a plurality of beam-forming networks, one for each of said columns of radiating elements, each of said beam-forming networks having a discrete output connected to each of said radiating elements in a corresponding column, each of said beam-forming networks also having a plurality of input ports each corresponding to a discrete beam angle in an axial plane containing said cylindrical axis and the corresponding column; for providing independent column zone feed means comprising a plurality of combining networks each having an input and a plurality of outputs, said outputs being interconnected with a predetermined plurality of adjacent input ports of a corresponding one of said beam-forming networks; scanning means comprising a plurality of orthogonal plane feed networks, each of said orthogonal feed networks having an input terminal and a plurality of output terminals each corresponding to a discrete beam angle measured in a plane substantially at right angles to said axis of said cylindrical array, each of said output terminals being connected to said input of one of said first combining networks corresponding to a discrete one of said column zones, thereby to produce a predetermined radiation pattern in said orthogonal plane; and means comprising a distribution network for connecting said orthogonal feed network input terminals to a common antenna system radio frequency terminal.
 3. The invention set forth in claim 2 in which said axis of said cylindrical array is substantially vertically oriented whereby said beam angles in said axial plane are elevation angles and said plane substantially at right angles to said axis is the azimuth plane.
 4. The invention set forth in claim 3 further defined in that the number of said combining networks and the number of said orthogonal plane feed networks and therefore the number of said independent column feed zones are all equal.
 5. Apparatus according to claim 4 in which said plurality of orthogonal plane feed networks is small compared to the number of ports of said beam-forming networks.
 6. Apparatus according to claim 5 in which the number of input ports of said beam-forming networks combined in each of said combining networks is substantially equal.
 7. Apparatus according to claim 5 in which said beam-forming networks are Butler matrices each having a number of said input ports equal to the number of radiating elements in the corresponding column.
 8. Apparatus according to claim 5 in which said beam-forming networks are series fed, equal path length beam forming networks having a predetermined number of ports and therefore being capable of providing a corresponding number of discrete elevation beam positions, said ports being fewer in number than the number of said radiating elements in the corresponding column. 